Studies directed toward the elucidation of the mechanisms of energy transduction and utilization in heart mitochondria will be conducted. The specific objectives will be to (1) determine the kinetics of the overall oxidative phosphorylation reaction, (2) further characterize adenine nucleotide-induced inner membrane contraction, (3) develop a method for specific depletion of mitochondria of endogenous adenine nucleotides, (4) determine the effect of intramitochondrial adenine nucleotide level on mitochondrial structure and function, and (5) determine the mechanism of energy-linked ion extrusion. Further characterization of adenine nucleotide-induced inner membrane contraction will include studies on the mechanisms by which inorganic phosphate, respiration, and ATP hydrolysis inhibit inner membrane contraction and on the relationship between rate of adenine nucleotide exchange across the inner membrane and rate and equilibrium magnitude of inner membrane contraction. The studies will be carried out with mitochondria isolated from slaughterhouse bovine hearts and will involve simultaneous monitoring of mitochondrial structure and function. Mitochondrial respiratory activity, mitochondrial optical density, and pH of the incubation mixture will be monitored simultaneously. State 3 rate of respiration will be used as an indicator of rate of oxidative phosphorylation and mitochondrial optical density as an indicator of change of inner membrane contractile status and of change of inner compartment volume due to influx and efflux of ions. Changes of mitochondrial structure and volume detected photometrically will be verified by electron microscopy and by determinations of mitochondrial packed volume.